Eigenmodes for masonry wall structures in Karamba 3D


I’m trying to model a 3-storey adobe building in Karamba3d. It is a load bearing structure so there are no columns or beams. The floor slabs are catenary vaults. I tried modeling the masonry walls as shell elements but the resulting eigenmodes do not reflect the mode shapes of multi-storey structures. I tried doing the same with columns then the mode shapes make sense. I also tried a third option where columns have no spaces in between them. Can someone help me with this?

Here is the link to the grasshopper definition.
eigenmodes_multistorey_masonry_walls_1.gh (152.9 KB)

Hi @Tahir_Zahid_Ishrat,
the eigenmodes and natural vibration modes show that your floor slabs are soft as compared to the rest of the structure.

To have one monolithic model is sometimes problematic: without joints between the elements (e.g. between floor slab and walls) the default connection is rigid in Karamba3D. If there is not a rigid but rather a hinged connection in the real structure the simulation thus overestimates the structural performance.

I would investigate the slabs in a separate model and check whether they are sufficiently stiff (take a look at the maximum displacement under service load and the first eigenfrequency which should be >3Hz for normal use and >5Hz for dance halls).

When you want to work with shallow vaults be careful to take into account cracking and creep which occurs over time. Also do not set horizontal supports which take the thrust and are not present in reality.

Walls simulated as 2d surfaces are very stiff. In reality there will be window openings and doors. I would rather use beam elements for the vertical loads and strategicaly placed bracings (either made from beam or shell elements) for horizontal loads. As long as the depth of the beams is less than two times the distance between 0-moment points (~ half the storey height) they give sufficiently precise results.

– Clemens